High-Capacity Rechargeable Li/Cl₂ Batteries with Graphite Positive Electrodes

Abstract

Developing new types of high-capacity and high-energy density rechargeable batteries is important to future generations of consumer electronics, electric vehicles, and mass energy storage applications. Recently, we reported ∼3.5 V sodium/chlorine (Na/Cl2) and lithium/chlorine (Li/Cl2) batteries with up to 1200 mAh g–1 reversible capacity, using either a Na or a Li metal as the negative electrode, an amorphous carbon nanosphere (aCNS) as the positive electrode, and aluminum chloride (AlCl3) dissolved in thionyl chloride (SOCl2) with fluoride-based additives as the electrolyte [Zhu et al., Nature, 2021, 596 (7873), 525–530]. The high surface area and large pore volume of aCNS in the positive electrode facilitated NaCl or LiCl deposition and trapping of Cl2 for reversible NaCl/Cl2 or LiCl/Cl2 redox reactions and battery discharge/charge cycling. Here, we report an initially low surface area/porosity graphite (DGr) material as the positive electrode in a Li/Cl2 battery, attaining high battery performance after activation in carbon dioxide (CO2) at 1000 °C (DGr_ac) with the first discharge capacity ∼1910 mAh g–1 and a cycling capacity up to 1200 mAh g–1. Ex situ Raman spectroscopy and X-ray diffraction (XRD) revealed the evolution of graphite over battery cycling, including intercalation/deintercalation and exfoliation that generated sufficient pores for hosting LiCl/Cl2 redox. This work opens up widely available, low-cost graphitic materials for high-capacity alkali metal/Cl2 batteries. Lastly, we employed mass spectrometry to probe the Cl2 trapped in the graphitic positive electrode, shedding light into the Li/Cl2 battery operation.

Shedding Light on Rechargeable Na/Cl2 Battery

“…3c, d), suggesting that the intercalation reactions were reversible. Similar intercalation peaks were observed in our recent studies of Li/Cl2 battery using a defective graphite material as the positive electrode 2 . The intercalating species could involve AlCl4 -• x AlCl3 (where x is a number and AlCl3 was released from NaAlCl4 complexes in the electrolyte upon NaCl electro-oxidization), as suggested in a similar study of electrochemical graphite chlorination and chlorine evolution in a NaAlCl4 melt electrolyte [29][30][31][32] .…”

“…chloroaluminate) species 33 . We suggest that upon charging the Cl2 species generated by NaCl electro-oxidation were mostly trapped in the micropores of aCNS, which also facilitated anion intercalation of the graphitic domains adjacent to the pores [1][2] . Related was that chloride intercalation into graphite only occurred when Cl2 was present in various vapor phase reactions 29,31,[34][35] .…”

“…Different types of rechargeable battery have been actively pursued using reactive metals as negative electrodes [3][4][5][6][7][8][9][10][11] . Recently we reported rechargeable Na/Cl2 and Li/Cl2 batteries in an aluminum chloride (AlCl3), fluoride-additive and SOCl2 containing electrolyte [1][2] . Reduction of SOCl2 in the first discharge afforded NaCl or LiCl deposited into the pores and surface of aCNS or defective graphitic carbon in the positive electrode, accompanied by Na or Li oxidation to Na + or Li + at the negative electrode.…”

“…Over cycling, redox reactions were complex involving SOCl2 oxidation and regeneration, but the main charge-discharge voltage plateaus were found to be reversible redox between Na/Na + or Li/Li + at the negative electrode and between Cl -/Cl2 at the positive electrode, with a discharge voltage of ~ 3.5 V and cycling capacity of up to 1200 mAh g -1 (based on the mass of carbon in the positive electrode) over up to 200 cycles [1][2] . Thus far, we found that amorphous carbon with high surface area/large pore volumes or in situ exfoliated defective graphite were important to high Cl2 trapping capability and rechargeability of alkali metal/Cl2 batteries, with the reversible chargedischarge capacity increasing with the pore volume of carbon [1][2] . Further investigations of alkali metal/Cl2 batteries are key to fundamental understanding of the battery chemistry and devising new strategies to improve battery performance towards practical use.…”

Concentrated Chlorine-Based Electrolyte Enabling Reversible Cl3–/Cl– Redox for Energy-Dense and Durable Aqueous Batteries

“…The high potential of anion insertion is also accompanied by the decomposition of electrolyte, further aggravating the batteries’ deterioration. , Fortunately, a great deal of progress has been made recently in this area to improve the reversibility of the Cl 2 /Cl – redox couple. Zhu et al , fabricated the amorphous carbon nanospheres and activated defective graphite which provide more active sites and effective trapping of Cl 2 than those of crystalline graphite materials. A nonpolar solvent carbon tetrachloride was selected by Hou et al to extract and store the oxidation products Cl 2 from aqueous electrolytes, which significantly enhances the Coulombic efficiency from 8.0 to 97.0%.…”